This invention pertains to methods for culling plants and the like and, more particularly, to a method for culling soybeans. The present invention teaches a method and apparatus for culling plants, such as soybeans, etc., directly on a harvesting apparatus, such as a combine or other crop harvesting equipment.
Soybean breeders typically make a cross between two varieties which are genetically dissimilar and advance the seed through generations of self pollination to a point were a single plant can be selected, which is, for the most part, homozygous at most loci and breeds true for the major traits of interest. Seeds from this plant and its subsequent generations are then tested for traits of interest including quantity and composition of protein and oil, resistance to pests (e.g., phytophthora root rot, soybean cyst nematode (SCN), brown stem rot, white mold, sudden death syndrome, stem canker, charcoal rot, etc.), appearance (e.g., lodging, pod load, and plant health), yield (usually by grain weight, volume of the grain or visual appearance), emergence (e.g., depth at which a line will emerge from or speed at which an individual emerges), nutrient deficiency or toxicity (e.g., iron deficiency chlorosis, zinc toxicity, maturity, height, molecular marker data (which are usually linked to one of the above traits of interest)), and other factors. The best individuals are kept and their progeny are tested in subsequent years until the few remaining lines are released for sale to farmers for growing. The most important factor is yield. Nevertheless, without considering the other factors, the variety may be undesirable or unusable. For example, without considering factors other than yield, the variety may not have the necessary protein or oil composition, or may produce unstable yields as pests attack the plants in different environments, or the plants may lodge so much that a farmer can not efficiently harvest the grain or finds that its appearance is objectionable.
To select lines, soybean breeders grow the progeny of a plant from a bulk population in a row called a progeny row or in a hill called a hill plot. Several such plots are grown from a population (the progeny from any one cross), and the best are selected by visual selection or by some measure of yield. The measure of yield is referred to in this present disclosure as a progeny row yield test (PRYT). Visual selection based on physically observing, or looking, at each row, is very subjective and requires a high degree of artistic talent by the breeder. Many experienced breeders believe that this technique is inefficient. In either case, a yield test of some type will be conducted in subsequent generations. A breeding program may have hundreds of thousands of individual genotypes to evaluate each year. PRYTs and other yield tests are highly laborious. The labor and expense involved in cataloging, planting, note taking, harvesting, transporting, analyzing, culling, and discarding this large number of samples is very high. Another disadvantage of the current yield test approach is the time required for harvest, analysis, selection, and getting the seed ready for shipment for replant in winter nurseries. At present, the seed industry is extremely competitive with new genotypes and traits emerging each year. The first company or entity to incorporate these traits into new varieties and to bring them to market receives a competitive advantage. Many seed companies, utilize winter nurseries in, e.g., Chile, Argentina, and Puerto Rico. To conduct meaningful tests when growing in these countries, seeds must be delivered to a testing site within a couple of weeks after they are harvested. Each soybean research station can have, e.g., 20,000 or more samples. As a result, it has been impossible to analyze, select, and cull these samples in the requisite time period with conventional means without a critical year loss in cycle time.
Current techniques include a crude culling technique wherein the yield of a sample, based on volume or weight of seeds, is compared to the yield of checks planted beside the same area as the samples of interest. The checks are harvested first, and a threshold value is marked on the cylinder or written down. All samples below the level of this threshold value are discarded. This technique has a number of disadvantages. In most crosses, the days required for soybean lines to mature varies. Lines taking longer to mature will usually have more growth and therefore out-compete earlier lines. Occasionally, the reverse can be true. Earlier lines can out-yield later maturity lines due to poor late season growing conditions or frost. For these reasons, very narrow maturity crosses are generally used with this technique. Another disadvantage is that although the checks may be planted in the general areas as the unselected lines, the size of the blocks may keep checks some distance from several lines that are selected. This means the checks do not adequately represent all the variation in the field, and the yield of the checks may therefore be unusable to compare to the unselected lines. One primary disadvantage of this technique is that selection is based only on yield and no other factors are taken into account. The price of the combines used to harvest these lines ranges from about $30,000 to well over $150,000. With the current method, a good operator can harvest one plot every 20-30 seconds and can do about 1000 plots/day. A common rule of thumb used in the industry is that the midwest will have 10 days fit for harvest. Therefore, one can expect to harvest 10,000 plots per year with each combine.
Selection indexes have been used by several individuals in several crops to select lines after all data has been collected, but not to select as data is being collected on a harvest apparatus. Computer programs which can generate selection indexes exist, but these programs have not been used to make selections while the data is being generated.